Method of manufacturing high emissive cathodes



Jan. 16, 1934. 5, W|ENEKE 1,943,945

METHOD OF MANUFACTURING HIGH EMISSIVE CATHODES Filed March 6, 1930 Jnveniar:

Patented Jan. 16, 1934 UNITED STATES PATENT OFFICE Bruno Wieneckc,Berlin, Germany Application March 6, 1930, Serial No. 433,846, and

in Germany March 8, 1929 2 Claims.

The manufacture of cathodes for electron valves, and especially multiplevalves, by the metal vapour process has hitherto met with variousdifficulties, including the difficulty created by the production of theemissive layer upon the cathode. The manufacturing process has generallybeen such that the substance arranged upon the anode was dispersed byheating the anode by means of an eddy current device, the dispersedsubstance precipitating upon the cathode which, whilst these operationswere proceeding, was preferably kept in a warm state. In the case ofmultiple valves with anode systems of different sizes, it appears thatthe dispersal cannot be effected in the same manner for the differentanodes. The system with the larger anode, i. e. generally the poweramplification stage, is heated much sooner and more intensely than thesmaller anodes. As a rule, therefore, only the cathode of the poweramplification stage is properly covered, while no emissive layer formson the cathodes of the voltage amplifying stages, because the heatgenerated in the anodes of the voltage amplifying stages by means of theeddy current device does not sufiice to disperse the substances whichhave been arranged in the pockets of the anodes. If the heating isproceeded with in such manner that the anodes of the voltage amplifyingstages, too, may be properly heated, the excessive heat may damage theanode of the power amplification stage. It may happen, too, that thecathode of the latter system is so strongly heated by the excessiveheating of the anode that the layer precipitated upon it evaporates.

It might be suggested that to overcome the difiiculties a constructionof the multiple valve might be adopted in which each system is heated byitself, i. e. independent of the others by a 40, single eddy currentgenerator. This construction is, however, not so simple as it mayappear. The construction of an eddy current device suitable for thispurpose is also difficult.

The present application proposes a different method attaining the sameend by a simpler process. According to the invention the elec trodesystems without prejudice to their dimensions in electrical respects,are constructed in such a manner that a single eddy current deviceproduces a uniform heating of the systems.

In the simplest case this aim is attained by the anode systems beinggiven the same crosssectional shape so that the flux encircled by theanodal areas is of a uniform size. If the anodes of the differentsystems are in electrical and thermionic respects of the same materialand if they are manufactured in the same way, the same eddy current heatwill be produced. A gradation of the different systems in electricrespects may be effected by an appropriate choice of the length, i. e.the length of the cathode, the grid and the anode.

The valve according to the invention is, however, not limited to thisconstruction. The enclosed flux is also uniform, if, with the same anodematerial and with the same thermic propperties of the anodes, especiallyin respect of the heat radiation, the cross-sectional areas of theanodes are the same. The shape of the different anodes, thus, may bedifferent. Thus one sys- (.6 tem may be flat, the other circular, thethird may have a rectangular shape, as long as the cross-sectional areasare of the same size. The measurement of the length is preferablygoverned by the electric power of the system.

A third group of multi-system and multiple valves is obtained if thecross-sectional areas of the different systems are different and thechoice of the metal for the anodes and their properties in thermicrespects are made in such a manner that an even heating is produced forthe same exciting alternating field.

Figs. 1-3 illustrate each an example of these three different groups,each example having two electrode systems.

Fig. 1 shows the cross-section through the vacuum vessel in which twoelectrode systems with like shapes of cross-section for anodes 2 and 3are contained. Perpendicularly to the level of the drawing the terminalamplifying stage 3 may, for instance, be longer than the voltageamplifying stage 2. Correspondingly the grid 4 of system 2 and theheating filament 5 may be of a length differing from that of the grid 6and heating filament 7 of the system 3. 95 There is the furtherpossibility of differing between the grids 4 and 6 and the filaments 5and 7 in yet other respects according to the requirements of theproperties of the system. Thus the grid 4 of system 2 will generallyhave a larger amplification factor than the grid 6 of system 3 and thatgrid will, as a rule, have a small amplification factor as, according toexperience, the voltage amplification requires a large and the poweramplification a small amplification factor. At 8 and 9 the substances tobe evaporated and precipitated on the cathodes 5 and '7 are arranged inpockets of the anode systems 2 and 3.

Fig. 2 also shows a cross-section through the discharge vessel 1 and thesystems 2 and 3. The latter differ in the shapes of theircross-sections, but have the same cross-sectional areas, the fluxenclosed by the anodes being therefore the same in both cases.

The cross-section through the discharge tube 1 in Fig. 3 shows 2 systems2 and 3, which are different in the shape and area oftheir crosssectionsand produce the same eddy current heat by an appropriate choice of thematerial and a suitable determination of the radiation factors.

In the above lines under eddy current device a high frequency inductioncoil disposed externally the envelope is understood. The electrodesinside the envelope are heated by the high frequency magnetic field ofthat coil.

I claim:

1. In an electron discharge device, several electrode systems, each ofsaid systems comprising a plate, a grid and a highly emissive cathode,said plates consists of the same material, having different lengths, across-section of the same area and a portion of a reaction mixtureattached thereto, which is to be heated by induced currents.

2. In an electron discharge device, several electrode systems, each ofsaid systems comprising a plate, a grid and a highly emissive cathode,said plates consisting of the same material, having different lengths, across-section of the same area and shape and a reaction-mixture attachedthereto, which is to be heated by induced currents.

BRUNO WIENECKE.

